Electric arc lamp



July 15, 1952 G, QBB 2,603,759

ELECTRIC ARC LAMP Filed Oct. 14, 1949 Patented July l5, 1952 Georges Lobb, Brussels, Belgium Application October 14, 1949, Serial No. 121,334 In Belgium October 29, 1948 (Cl. B14-31) 3 Claims.

The present invention relates to electric arc lamps, particularly those designed for projecting fixed or animated pictures.

The arc lamps customarily utilised for this purpose have two carbons, supplied eithei` with continuous current or with monophase alternating current. Whatever the nature of this supply may be, these lamps have numerous disadvantages.

`As rdistribution is generally effected in the form of alternating current, continuous current lamps necessitate a device for commutation or rectification of the current. Lamps supplied with monophase current furnish a pulsating light, the frequency of which often interferes, in the case of cinematographic projections, with the frequency of obturation of the image, thereby occasioning variations in the illumination of the latter.

On the other hand, the arrangement of the two carbons in relation to the concave mirror of these lamps is such that the unavoidable irregular-ities in the combustion of the carbons produce a displacement of they luminous point, which has to be corrected by the aid of manual controls, at the cost of constant supervision.

The carbons furthermore necessitate the mounting of supports, which intercept a substantial part Aof the beam of useful light. The mirror itself has to be pierced with a central hole forthe passage of the carbon and of its support, thereby reducing thel useful reflecting surface area. Moreover the light utilised, which comes mainly from the crater of the arc, is more intense at the centre than on the edges, and this inequality is carried over to the screen on to which the picture is projected.

It has also been proposed to make use of arc lamps with a plurality of parallel carbons, but these lamps cannot be suitable for the projection of pictures, as the abovementioned disadvantages still manifest themselves to an even more marked extent. Y

The object of the present invention is to eliminate all these disadvantages. To this end the lamp according to the invention comprises at least three carbons, arranged in star formation, either in one and the same plane or along the edges of a trihedron, a tetrahedron, etc., and supplied with polyphase alternating current.

In carrying thelinvention into practice, the carbons are carried by grippers or collars, which are preferably arranged outside the useful beam of light, and which can each be displaced in the longitudinal direction of the carbon that it is I holding, in order to advance the latter progressively as it burns away. It is possible, according to requirements, to make use of a device such as a mirror or lens, to collect the light over a given angle in order to concentrate it towards the place to be illuminated. An automatic carbonfeeding device may likewise be utilised if ydesired.

According to one feature of the invention an arc-stabilisingv electro-magnet is so arranged that it includes the luminous point in its field, so as to produce a directive effect on the llame.

f The winding of this electro-magnet is traversed by an alternating current of the same frequency as that feeding the arc.

The accompanying drawings show diagrammatically two examples of construction of the invention, each with three carbons supplied with three-phase current.

Figure 1 represents the device as seen-from the. front;

Figure 2 is a corresponding profile view; and

Figure 3 is a proiile View showing a modification of the carbon-feeding mechanism.

v In Figures 1 and 2, the three carbons, arranged at degrees from one another, are represented at I, I', I", and are :mounted in collars 2, 2'., 2" respectively, which are displaceable on slideways or guides 3, 3. 3, under the actionof screws 4, l4', 4, set in rotation at an appropriate speed by motors 5, 5', 5, through the medium of speed-reducing transmission means. v

The arc is struck between the inner extremi ties of the carbons, opposite to the mirror 6, which is carried by a housing l. It is supplied with trihexaphase current at a suitable voltage, either directly, or through the medium of a voltage-transformer I3 when the voltage of the mains is too high to be directly utilisable.

At I4 is indicated an arc-stabilising electromagnet, consisting of a bar of iron placed between two of the carbons and orientedradially like the latter, so as to include the arc in its iield. the beam of light this bar is surrounded by a winding I5, which, in the example illustrated, is connected in series with one of the carbons, but might be connected in parallel between two carbons, or energised from a separate winding of the transformer for example.

In the modification according to Figure 3, the carbons I, I', I, the collars 2, 2', 2" and the slideways 3, 3', 3 occupy the same positions as in Figure l, but the collars are actuated simultaneously by a single motor 5, which, through the medium of a speed-reducer, rotates the drum 8, which in its turn drives drums 9, Il', 9 by means of cables, of which only two, IU and IUK',

' are visible in Figure 3. These drums'are rigid In the portion thereof situated outside with pinions Il, ll', H", which, through the medium of racks l2, l2', I2", effect the simultaneous displacement of the carbon-holding collars.

The device according to the invention functions with an excellent eiiiciency. Moreover the stability of the illumination is ensured, for the light furnished pulsates at such a frequency that the depth of pulsation is as restricted as that of an appliance furnishing continuous current. In fact since the arc is fed with threephase current, and each half-period is lightproducing, the pulsation is six-phase, so that the depth of pulsation is greatly attenuated.

The carbon-holders are outside the useful cone of light, and cannot therefore intercept the light rays. The mirror has no central hole, and the whole of its reecting surface is utilised.

On the other hand, thanks to the arrangement of the carbone, the luminous point is stationary by construction, and even in the event of irregular combustion of the carbons it will remain centered owing to the automatic advance of the carbons, which compensates for the wear thereof.

Contrary to what occurs with the usual arcs, it is not the light issuing from the crater that is primarily utilised, but mainly that of the name, Which, being struck between the three carbons, assumes, in the plane perpendicular to the optical axis, a very nearly circular form, thereby ensuring great regularity in the illumination of the image.

Instead of three carbons, the lamp according to the invention may comprise a greater number, four for example, which would be supplied with two-phase current. In the case of a threephase supply, the latter would be transformed into two-phase by means of a Scott-connected transformer. advantages of the three-electrode lamps that has been described by way of example, which constitutes the preferred embodiment of the invention.

It will be evident that other modifications may be made in the device described without going outside the ambit of the invention. The absence of any mechanism in front of the arc also allows of all desirable forms and arrangements for the light box. lodge therein the device for protection against fire, particularly in the case of cinematograph projectors Iclaim:

1. An electric arc lamp comprising a reflector housing open at one side, three equally angularly spaced carbon holders supported from the periphery of said housing at the open side thereof, an elongated carbon electrode in each of said holders extending radially toward the center of said housing, the inner ends of said electrodes being spaced apart to define an arc gap area therebetween, means supplying polyphase alternating electric current to said electrodes, an arc-stabilizing electro-magnet for directing the arc including a radially extending elongated magnetic core disposed between an adjacent pair of said electrodes in axial alignment with the third of said electrodes and a coil on the outer end of said core exteriorly of said housing, means energizing said coil, and a reector in said housing facing toward the open side of the latter behind said electrodes wherebyv said carbon holders and said coil are Such a lamp exhibits most of the It is also possible to disposed. outside the cone of useful light and do not intercept the reiiected light rays.

2. An electric arc lamp comprising a reflector housing open at one side, at least three equally angularly spaced guides extending radially inward from the periphery of said housing at the open side of the latter, a carbon holder slidable radially on each of said guides, an elongated carbon electrode in each holder, said carbon electrodes being disposed in the respectiVe radial planes of the related guides with their inner ends being mutually proximate to denne an area in which an arc may form, means supplying polyphase alternating current to said carbon electrodes, an arc-stabilizing electromagnet including a radially extending elongated magnetic core disposed between an adjacent pair of said electrodes in axial alignment with the third of said electrodes and an energizing coil on the outer end'of said core exteriorly of said housing, electrical means energizing said coil, a reilector in said housing facing toward the open side of the latter and behind said electrodes, and means for simultaneously moving said holders on said guides to effect adjustment of the spacing of the inner ends of said electrodes, said means including radially extending actuating members operatively connected to said holders and movable in said radial planes of the guides so that each electrode is in line with its respective guide and actuating member to present the minimal obstruction to the path of the light beam reiiected by said reflector.

3. An electric arc lamp comprising a housing opening at one side, at least three equally angularly spaced guides extending radially inward from the periphery of said housing at the open side of the latter, a carbon holder slidable ra.- dially on each of said guides, an elongated carbon electrode in each of said holders, said carbon electrodes extending radially in the planes of the respective guides and with their inner ends being mutually proximate to define an area in which an arc may form, means supplying polyphase alternating current to said carbon electrodes, a reflector in said housing facing toward the open side of the latter behind said electrodes, and means for simultaneously moving said holders on said guides to effect adjustment of the spacing of the inner ends of said electrodes, said means including radially extending actuating members operatively connected to said holders and movable in said planes of the respective guides so that the groups of guides, electrodes and actuating members are disposed in the same radial planes to present the minimal obstruction to the beam of light projected by said reflector, each of said actuating members including a radially movable gear rack fixed at its inner end to the related electrode holder, the means for simultaneously moving said holders including simultaneously driven spur gears mounted exteriorly of said housing and meshing with the respective gear racks.

GEORGES LOBB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,329,132 Miller Jan. 27, 1920 1,581,357 MacCorrnac Apr. 20, 1926 2,040,215 Rava May 12, 1936 2,046,117 Guest June 30, 1936 

